This invention relates generally to vehicle propulsion systems and, more particularly, to a hybrid gas turbine engine and flywheel propulsion systems for automotive vehicles.
Gas turbine engines are attractive for many vehicle propulsion applications because of their excellent fuel economy at full power, relatively low mass, low exhaust emission levels, and fuel versatility. However, gas turbine engines are less than ideally suited for automotive propulsion applications because, among other reasons, typical automotive duty cycles require engine operation for extended periods at low power levels where gas turbine engines encounter fuel economy penalties, rapid response to operator command comparable to internal combustion engines is required and not typically available, and low material and manufacturing costs are necessary for competitive reasons but difficult to achieve. Accordingly, numerous gas turbine engine configurations have been proposed which address various ones of the problems inherent in automotive applications. For example, in U.S. Pat. No. 3,981,140, issued Sept. 21, 1976 to Lunsford et al and assigned to the assignee of this invention, a single shaft gas turbine engine with improved compactness, lower mass, and lower associated costs than two-shaft engines is disclosed and includes variable geometry at the turbine nozzle, the compressor inlet, and the compressor diffuser for increased economy at low power levels. Also, in U.S. Pat. No. 3,097,485, issued July 16, 1963 to Joseph Bidwell and assigned to the assignee of this invention, a hybrid gas turbine engine and flywheel system is disclosed which overcomes the inherent lack of responsiveness in gas turbine engines through the use of a flywheel arrangement. In addition, commencing at page 81 of Naval Engineers Journal, issue of December, 1974, Dr. -Ing. N. Gasparovic describes performance improvements achieved in naval propulsion gas turbine engine applications where turbine motive fluid is expanded through one or more turbines from superatmospheric or superambient pressure to subatmospheric or subambient pressure and then compressed in a secondary compressor back to ambient pressure for exhaust to atmosphere. A hybrid gas turbine engine and flywheel propulsion system according to this invention represents a new and improved combination of a flywheel type energy storage unit and a subambient pressure cycle gas turbine engine which combination is particulary suited for automotive applications.